1. Field of the Invention
The present invention relates to hoisting means and, more particularly, to a hoisting assembly for the releasable connection of a hoisting harness to a precast concrete building element by means of a quick-release hoisting shackle cooperating with an anchoring member which is permanently embedded in the precast concrete element, for the tilt-up and transport of the precast element.
2. Description of the Prior Art
A quick-release hoisting shackle of the type referred to above is known from the German Pat. No. 22 40 171 and from the corresponding U.S. Pat. No. 3,883,170. Special anchoring members for the tilt-up of precast concrete elements with this hoisting shackle are suggested in the German Pat. No. 27 20 148 and in the corresponding U.S. Pat. No. 4,173,856.
The known hoisting shackle consists of a shackle body in the shape of a hollow torus, an arcuate locking bolt being guided for displacements inside its circular cavity. The locking bolt is movable between a locking position in which it is engaged across an eye hole in the eye portion of the embedded anchoring member and a release position in which the shackle body, which has a transverse slot receiving the eye portion, is engageable over and removable from the eye portion of the anchoring member.
The anchoring member is a "lost anchor", being positioned below the edge surface of the precast concrete member. The exposed eye portion of the anchoring member is located within an oblong engagement recess which approximately matches the shape of the shackle body.
Connecting the hoisting shackle to a hoisting harness is an attachment link which resembles a large chain link with two transverse apertures, the larger upper aperture serving for the engagement of a hook or cable sling of the hoisting harness and the smaller lower aperture receiving the upper portion of the shackle body. The attachment link remains attached to the hoisting shackle.
The tilt-up anchoring members which are suggested in U.S. Pat. No. 4,173,856 have an eye portion with a shape that includes one central or two laterally spaced longitudinal extensions or noses which cooperate with the shackle body in such a way that the latter remains substantially aligned with the anchoring member, even if pulled in a direction which is inclined as much as 90.degree. from the axis of the anchoring member.
This device makes it possible to tilt a precast concrete component from its initially horizontal orientation into a vertical orientation in which it is to be transported and/or installed, while preventing the shackle body from bearing against the flank of the engagement recess in the horizontal orientation of the precast member. This feature is necessary, in order to prevent spalling of the concrete in the area of the engagement recess, especially in the case of a thin precast element.
It has now been found that, in the case of certain precast concrete components, the known combination of a hoisting shackle with a special tilt-up anchoring member, as described above, has some shortcomings in connection with tilt-up operations, especially when the precast element has an edge profile with a protruding lip, or when it is necessary to recess the anchoring member as deeply as possible from the edge of the precast element. Both conditions are encountered in connection with thin precast plates which are used for walls and ceilings.